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3. Can Tesla somehow design the Powerpacks in such a way that they can output higher charge rates than the utilities can provide? Sort of a "super capacitor" if you will.

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I don't know about that but I thought I read somewhere that they cut the expense of some superchargers by reducing the demand charge. Some utilities charge a fee based on the highest kWh load in any 15 minute period.

In the past, Tesla has said that Supercharger usage has 2 peaks, Friday afternoon, as people leave for weekend trips, and Sunday, when they return. The rest of the time, most Superchargers are essentially unused.

This (eventually, if usage remains similar) leaves them with large amounts of grid connected storage during peak energy usage during most of the week. If they can make agreements with utilities to provide power during peak usage (where electricity can be $$/kWh if customers are hit with demand charges), to supplement/replace peak production, this could be the way the monetize the supercharger network, and still provide free electricity to Tesla drivers. It would create a more stable, less wasteful power grid. The size of a Supercharger network required to support Model 3 levels of cars would have a huge amount of storage, and would be better able to deal with peak demand than current peaker power plants.

At the 2014 Energy Storage Symposium JB Straubel gave a keynote address. This is the relevant section, starting at 24:15 in this You Tube video.

We have started piloting these installations and the controls for them with our own needs and applications and Supercharge is the perfect application for energy storage. It's big enough that we can really justify a lot of investment in controls and the hardware to optimize a single site. It's incredibly peaky load. You know, it's probably one of the worst loads. We're also paying the meter and paying the bill on this, you know Tesla funds this 100% and it's free to customers. So, we have our own demand charge [from the utility] we have our own utility interconnection and everything else. So, we get the benefits of course, of doing things like this if we can install storage and control it properly. Just to kind of look at what that looks like at Tejon, this is sort of a cool graph from very recently, it was just I think earlier this week, but you can kind of see ah, maybe pick apart this bottom graph here. The blue graph, the top line, is what the site would do if there was no energy storage. It's just the straight demand for electricity from the Superchargers going out to the cars. You see a spike of over a quarter megawatt, so that must have meant that there were probably around three or four cars Supercharging simultaneously at different states of charge and power. But that's a pretty big peak and it's really really short. You know, that's a peak that would only be about 20 minutes, so we might just be over the limit of it ratcheting to a peak demand for the entire month just when 3 or 4 cars happen to come together. That's something you really want to knock down. And then, in this case the red is the resulting meter import. So, that's the resulting load of the site after the battery has contributed to it and you can see the huge difference. The green is the battery support. So, the battery in this case, ah, this is about a, um, maybe about a 300 kilowatt peak battery pack, so it's knocking down a majority of this peak and we get to a load profile that's actually, you know, reasonably continuous. Even though cars are coming and going, charging at 100 kilowatts plus, one after the other, some of them overlapping. So, this has been a really great proof of concept for us and it's taken a while to work out the controls so this actually works well and happens smoothly, but it's, I think, a wonderful example of a really clear economic viability for energy storage. So, we're rolling this out at almost all the Supercharge sites, you know, over time. This was the very first and we're continuing to do more.

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3. Can Tesla somehow design the Powerpacks in such a way that they can output higher charge rates than the utilities can provide? Sort of a "super capacitor" if you will.

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I don't think Tesla would install an energy storage system so that the draw could be larger than what the utility can provide, but they will certainly avoid a lot of demand charges by using energy storage.

Yes, I knew they were similar to those used at Superchargers. This version is only good for 400kWh. The Tesla Energy engineer told us that the firmware is designed to limit charging from 10% to 90% state of charge. This is fixed by Tesla and can not be modified by the purchaser, in this case Duke Energy.

2. Will some of the lightly used Superchargers produce more energy than they consume and become profit centers of energy?

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Perhaps in states that permit net metering the host might benefit. In Florida this isn't currently permitted. In the installation that I referenced using Tesla battery storage, the benefit goes straight to the utility who paid for the installation, not the host university.

3. Can Tesla somehow design the Powerpacks in such a way that they can output higher charge rates than the utilities can provide? Sort of a "super capacitor" if you will.

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The charge rate of our cars are already limited by the battery chemistry and programmed into the car's firmware accordingly. I have an A battery and it will only charge at up to 90 kW. Other cars are limited to 120 kW.

If they wanted the battery storage system to deliver capacity greater the local utility supply and greater than the current Supercharger capacity I guess that there would have to be switching and control circuitry added to bypass the Superchargers and go directly to the charging terminals. Otherwise that DC current would have to be converted back to AC and delivered to the Supercharger, but then the Supercharger would have to have additional chargers in the stack to handle the additional capacity.

As a side note, in situations where Superchargers experience congestion, regardless of how the added capacity is supplied, there would be some benefit in having Supercharger capacity in excess of what an individual car could handle. The car's firmware would continue to regulate the charging rate consistent with what its battery can handle. However, in a congested station the added capacity could be shared between charging terminals at a higher average rate. The net result would be greater average throughput through the Supercharger Station even though individual cars never exceed their rated maximum allowed capacity.

I bet the 12 charger modules used in each SC cabinet can easily accept DC directly from the storage battery with just a simple relay needed on each one to toggle between AC 277V and DC. When the SC's aren't in use, another relay on the output of the SC can select charge from the SC to the battery. Thus with only a control board and a handful of relays, they have a pretty simple addition. It would be silly to invert the output of the battery to 277VAC only to have it taken back to DC in the front end of the charger module.

I bet the 12 charger modules used in each SC cabinet can easily accept DC directly from the storage battery with just a simple relay needed on each one to toggle between AC 277V and DC. When the SC's aren't in use, another relay on the output of the SC can select charge from the SC to the battery. Thus with only a control board and a handful of relays, they have a pretty simple addition. It would be silly to invert the output of the battery to 277VAC only to have it taken back to DC in the front end of the charger module.

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The chargers only accept AC input. I do think converting DC to AC then back to DC is silly. I'm just trying to imagine the interconnect sound when trying to do that. Also, how would you modulate the power if you're going DC to DC?

The Tesla charger module input section's front end is a bridge rectifier, thus the first thing they do is to convert incoming 277VAC into 370VDC. This is then boosted for PFC (Power factor correction) to probably around 400-450VDC with a non-isolated boost converter, then it's sent to the isolated switch mode supply to generate the final 50-410VDC output for charging. Unless Tesla specially created a firmware check to inhibit operation without AC input, then there is no reason the system wouldn't run fine on DC. (And of course Tesla could remove this check on the SC firmware)

Most AC switch mode supplies, such as the kind Laptops and Cell phone chargers use, work quite fine on DC for the same reason.

There is no need to "modulate" power anywhere else, as this is what the SC already does quite fine. The only difference is that it's using the battery bank instead of the 277V line.